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Reactive molecular dynamics of network polymers: Generation, characterization and mechanical properties.

机译：网络聚合物的反应性分子动力学：生成，表征和机械性能。

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摘要

The goal of this research was to gain a fundamental understanding of the properties of networks created by the ring opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) used in self-healing materials. To this end we used molecular simulation methods to generate realistic structures of DCPD networks, characterize their structures, and determine their mechanical properties. Density functional theory (DFT) calculations, complemented by structural information derived from molecular dynamics simulations were used to reconstruct experimental Raman spectra and differential scanning calorimetry (DSC) data.;We performed coarse-grained simulations comparing networks generated via the ROMP reaction process and compared them to those generated via a RANDOM process, which led to the fundamental realization that the polymer topology has a unique influence on the network properties. We carried out fully atomistic simulations of DCPD using a novel algorithm for recreating ROMP reactions of DCPD molecules. Mechanical properties derived from these atomistic networks are in excellent agreement with those obtained from coarse-grained simulations in which interactions between nodes are subject to angular constraints. This comparison provides self-consistent validation of our simulation results and helps to identify the level of detail necessary for the coarse-grained interaction model.;Simulations suggest networks can classified into three stages: fluid-like, rubber-like or glass-like delineated by two thresholds in degree of reaction alpha: The onset of finite magnitudes for the Young's modulus, alphaY, and the departure of the Poisson ration from 0.5, alphaP. In each stage the polymer exhibits a different predominant mechanical response to deformation. At low alpha alphaY it flows. At alpha Y alpha alphaP the response is entropic with no change in internal energy. At alpha > alphaP the response is enthalpic change in internal energy.;We developed graph theory-based network characterizations to correlate between network topology and the simulated mechanical properties. (1) Eigenvector centrality (2) Graph fractal dimension, (3) Fiedler partitioning, and (4) Cross-link fraction (Q3+Q4). Of these quantities, the Fiedler partition is the best characteristic for the prediction of Young's Modulus. The new computational tools developed in this research are of great fundamental and practical interest.
机译：这项研究的目的是对自愈材料中使用的双环戊二烯（DCPD）的开环易位聚合（ROMP）所形成的网络的性质有基本的了解。为此，我们使用了分子模拟方法来生成DCPD网络的真实结构，表征其结构并确定其机械性能。使用密度泛函理论（DFT）计算以及分子动力学模拟得出的结构信息来重建实验拉曼光谱和差示扫描量热法（DSC）数据;我们对粗粒模拟进行了比较，比较了通过ROMP反应过程生成的网络并进行了比较它们到通过RANDOM过程生成的那些，最终导致人们认识到聚合物拓扑结构对网络属性具有独特的影响。我们使用新颖的算法对DCPD分子进行了完全原子模拟，以重新创建DCPD分子的ROMP反应。从这些原子网络得出的机械性能与从粗粒度模拟获得的机械性能非常一致，在粗粒度模拟中，节点之间的相互作用受到角度约束。这种比较为我们的仿真结果提供了自洽的验证，并有助于确定粗粒度交互模型所需的详细程度。仿真表明，网络可分为三个阶段：描绘出的流体状，橡胶状或玻璃状通过反应度α的两个阈值：杨氏模量αY的有限幅度的开始以及泊松比从0.5αP的偏离。在每个阶段，聚合物对变形表现出不同的主要机械响应。当alpha alphaP时，响应是内部能量的焓变。；我们开发了基于图论的网络表征，以将网络拓扑与模拟的机械特性相关联。 （1）特征向量中心点（2）图的分形维数，（3）Fiedler划分，以及（4）交联分数（Q3 + Q4）。在这些数量中，Fiedler分区是预测杨氏模量的最佳特征。在这项研究中开发的新的计算工具具有重大的基础和实践意义。

著录项

  • 作者

    Shankar, Chandrashekar.;

  • 作者单位

    University of Michigan.;

  • 授予单位 University of Michigan.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 201 p.
  • 总页数 201
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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